The present invention relates to a data transfer control device, electronic equipment, and a data transfer control method.
The universal serial bus (USB) standard 2.0 is expanding well in the marketplace, but an interface standard called the USB On-The-Go (OTG) has been settled upon by the USB Implementers Forum (USB-IF). The OTG standard (OTG 1.0) that has been derived as an extension of USB 2.0 holds out the possibility of bringing new additional value to the USB interface, and it is expected that applications that make use of these characteristics will appear.
This OTG makes it possible to impart a host function to a peripheral (peripheral device) connected to a host (such as a personal computer) by existing USB. This makes it possible to transfer data between peripherals connected by USB, enabling direct connection between a digital camera and a printer, by way of example, so that an image from the digital camera can be printed. It is also possible to connect a digital camera or digital video camera to a storage device, to save data therein.
However, it is usual for a peripheral that is given the host function by OTG to have a limited-capability CPU (processing section) incorporated therein. The addition of the host function therefore places a heavy processing load on the CPU (firmware) of the peripheral, making processing complicated and raising further problems such as impeding other processes and lengthening the design period of the device.
Four types of transfer are defined by the various USB standards such as USB 1.1, USB 2.0, and OTG: isochronous transfer, bulk transfer, control transfer, and interrupt transfer. A USB host manages the transfer sequence of packets of each of these transfer types, and transfers packets of each transfer type while considering the remaining time in each frame. For that reason, the host performs frame management under USB, so that the host transfers a start-of-frame (SOF) packet to the peripheral every 1 ms at full speed (FS) or low speed (LS) or 125 μs at high speed (HS).
It has become clear that with non-periodic transfers such as bulk transfer or control transfer, however, the transfer of such a SOF packet has the result of reducing the bus bandwidth, which raises the problem of a drop in transfer efficiency.